polynomial regression where x = day, y = cost

polynomial regression degrees 2-4

## Method

The polynomial regression can be generated by the **RDOUBLE** formula below.

The function in the example below is for a polynomial regression of the third degree.

If you require a function of a different degree, simply edit the **3** in the poly function to whichever degree you need.

## Formulation

To keep this approach generalized, I did not convert the values to a time series (ts). Instead, I used the rank function to convert each x-axis element to a vector of 1-*n* by using the RANK function.

rdouble(FALSE, "

x <- args[[2]];

y <- args[[1]];

model <- lm(y ~ poly(x,3));

predict(model);

", [Total Cost], rank(max([Months in Date]), "ASC", "1223"))